Pentax 645D Exposure

Saturation & Hue Accuracy
Very accurate default saturation with good hue accuracy.

Saturation. The Pentax 645D's default "Natural" image tone setting produces images with very accurate saturation, just slightly oversaturated by only 0.3% overall. Dark blue, dark green and dark brown are pushed just slightly, while most other colors are practically dead-on or slightly desaturated. Some may think the 645D's colors are a bit dull, but they are more faithful than most cameras. You can of course always select a different image tone preset (see below) and/or adjust settings such as saturation and contrast to suit your own tastes. Most consumer digital cameras produce color that's more highly saturated (more intense) than found in the original subjects. This is simply because most people like their color a bit brighter than life.

Skin tones. Caucasian skin tones from the Pentax 645D were a touch yellow using auto white balance, while manual white balance produced a more pinkish, "healthier" appearance. Where oversaturation is most problematic is on Caucasian skin tones, as it's very easy for these "memory colors" to be seen as too bright, too pink, too yellow, etc.

Hue. The Pentax 645D showed a few color shifts relative to the correct mathematical translation of colors in its subjects, but had good accuracy overall when using default settings. Most noticeable were shifts in orange toward yellow and cyan towards blue, with some very minor shifts to other colors. (The cyan to blue shift is very common among the digital cameras we test; we think it's a deliberate choice by camera engineers to produce better-looking sky colors.) The 645D's "delta-C" hue error after correction for saturation is 4.71, which is slightly better than average. Some SLRs have scored in the mid-3's (lower numbers are better), so the 645D's hue accuracy isn't outstanding, but it's still pretty good. Hue is "what color" the color is.

Custom Image
The Pentax 645D offers nine preset "Custom Image" options. You can adjust Saturation, Hue, High/Low Key, Contrast, Sharpness, Filter Effects and Toning parameters from -4 to +4 (9 steps). Some adjustments are not available depending on the Custom Image type.

Mouse over the links above to see the effect of the presets on our Still Life target. Click on a link to load the full resolution image.

Saturation Adjustment
The Pentax 645D lets you adjust image Saturation in nine steps. As can be seen below, the saturation adjustment worked well, providing a reasonably fine-grained adjustment over a useful range of control. The saturation adjustment also has almost no impact on contrast. That's how a saturation control should work, but we've often found interactions between saturation adjustments and image contrast (and vice versa) on the cameras we test.

The series of shots above shows results with several different saturation adjustment settings, showing the minimum step size around the default, as well as both extremes. See the Thumbnails index page for more (look for the files named 645DOUTBSATx.JPG). Click on any thumbnail above to see the full-sized image.

Exposure and White Balance

Indoors, incandescent lighting
Very warm results with Auto white balance, though good color with Incandescent and Manual white balance settings. Slightly above average exposure compensation required.

The Pentax 645D's default Auto white balance had a difficult time with the very warm color balance of the household incandescent bulbs used in this shot. Like other more recent Pentax SLRs, the 645D offers two settings for Auto white balance correction in Tungsten light: Subtle which is the default setting, and Strong. We unfortunately don't have results with Strong correction, but it helped on other Pentax bodies. Results with the Incandescent setting were pretty good, just bit on the cool side. The 2,600 Kelvin setting which should match our tungsten lamps produced a strong greenish cast. The Manual setting produced the most accurate results, though still a touch cool. Note that the 645D also has a Color Temperature Enhancement (CTE) white balance mode, which strongly intensified the orange/yellow cast in our indoor test shot on other Pentax bodies. We didn't try that option for the 645D. The Pentax 645D required +0.7 EV exposure compensation for a bright image, which is a little higher than the +0.3 EV average required for this shot. Our test lighting for this shot is a mixture of 60 and 100 watt household incandescent bulbs, a pretty yellow light source, but a very common one in typical home settings here in the U.S.

Outdoors, daylight
Good color with very good exposure, though somewhat high default contrast.

The Pentax 645D handled tough outdoor lighting under harsh sunlight fairly well, producing bright images with fairly accurate exposure. Default contrast was a bit on the high side (as most users prefer), leading to some clipped highlights. +0.3 EV exposure compensation was required to keep the model's face bright (the default exposure was a tad dim), which is better than the average of +0.7 EV usually required for this scene. Skin tones were just a touch yellow using auto white balance, so we preferred manual white balance for outdoor portraits. The house shot was also well exposed at 0 EV, but also with quite a few clipped highlights in the white trim, though shadows were very good. Color was just a touch cool using Auto white balance. Still, fairly good results here.

See full set of test images with explanations
See thumbnails of all test and gallery images

Resolution
Extremely high resolution, ~3,700 lines of strong detail from JPEGs, about the same from converted RAW files.

Our laboratory resolution chart revealed sharp, distinct line patterns down to about 3,700 lines per picture height in the horizontal direction about 3,7000 lines per picture height in the vertical direction in JPEGs. Complete extinction didn't occur before the 4,000 line limit of our chart. RAW files processed through Adobe Camera RAW showed more distinct lines, but color moire was much higher. Color moire is even more of a concern with the 645D as it doesn't have an anti-alias filter, though its JPEG engine does a great job at suppressing it here. Use these numbers to compare with other cameras of similar resolution, or use them to see just what higher resolution can mean in terms of potential detail.

See full set of test images with explanations
See thumbnails of all test and gallery images

Sharpness & Detail
Sharp images with exquisite detail, though with minor edge-enhancement on high-contrast subjects. Minor noise suppression visible at base ISO.

Sharpness. The Pentax 645D produced sharp images with phenomenal detail at default settings. Some minor edge enhancement artifacts are visible on high-contrast subjects such as some of the branches in the crop above left, but overall results are quite amazing. Edge enhancement creates the illusion of sharpness by enhancing color and tonal differences right at the edge of a rapid transition in color or tone.

Detail. The crop above right shows some minor detail loss due to noise suppression, as the darker areas of the model's hair still show very good detail. Individual strands are distinguishable even in the lighter shadows, though they begin to merge as shadows deepen, and in places where the tone and color of adjacent strands is very close. Still, very good results here. (Remember, we're looking at a 40-megapixel image at 100% here.)  Noise-suppression systems in digital cameras tend to flatten-out detail in areas of subtle contrast. The effects can often be seen in shots of human hair, where the individual strands are lost and an almost "watercolor" look appears.

Aliasing. The Pentax 645D's CCD sensor is not covered with an optical anti-aliasing (low-pass) filter that is normally used to intentionally introduce subtle blurring to reduce moire and other aliasing artifacts in most Bayer color filter cameras. This of course means per-pixel sharpness of the 645D's images is superb, but it also means that aliasing artifacts are more likely. Pentax says the 645D instead combats such image defects using software techniques and lens design, and indeed we didn't find aliasing to be as big of an issue as we expected. That's not to say we didn't notice some aliasing artifacts in a number of 645D images we shot. The 100% crops at right for instance show obvious moire patterns and aliasing, and there are instances of aliasing artifacts in other 645D lab and gallery images. (See the orange fencing in this gallery shot for a real-world example.) To be fair, we've seen similar artifacts from other high resolution cameras with weak low-pass filters, so it's not something unique to the 645D. It's just something that's more likely to occur with the 645D, especially when shooting with sharp lenses stopped-down a bit from maximum aperture.

Minor pixel column defects. As mentioned elsewhere in our 645D review, sometimes our test targets show minor sensor defects that are virtually invisible in real-world images. For example, the sharp black/white contrast of the resolution chart often shows artifacts from the pixel-substitution used to fill in for faulty sensor pixels. In the case of the 645D, an artifact of this sort appears in our resolution and our viewfinder accuracy test target images, at pixel column 2799. The 100% crops at right show the effect of this defect. We call this a "minor" sensor defect, because the results are actually incredibly hard to see in images of real-world subjects. This is pretty much of a non-issue, unless your business is photographing test charts. Note that a second 645D we tested showed similar defects in different columns, so Pentax must also believe this is a very minor issue.

RAW vs In-Camera JPEGs
As noted above, the Pentax 645D does an excellent job at capturing gobs of detail in its JPEGs, but believe it or not, more detail can be obtained from carefully processing RAW files, without introducing additional artifacts. Take a look below, to see what we mean:

In the table above, mousing over a link at the bottom will load the corresponding crop in the area above, and clicking the link will load the full resolution image. Examples are shot at ISO 200, and include in-camera Premium JPEG as well as the matching RAW file processed through Adobe Camera Raw (ACR) version 6.3, then sharpened in Photoshop. For the Pentax 645D's RAW files, we found best results with fairly light but tight 250% unsharp masking with a 0.3 pixel radius.

As is frequently the case, the demosaicing and sharpening in Adobe Camera and Photoshop deliver finer detail than the camera. Looking very closely at the images, ACR extracts more detail that wasn't present in the JPEGs, but renders colors and contrast differently than the default camera settings, and there's also a bit more noise visible. You can always adjust RAW image rendering to your liking, though, which is one of the advantages of shooting RAW and processing the images yourself.

ISO & Noise Performance
Very good handling of noise vs detail across the entire ISO range.

The Pentax 645D's images were very clean at ISO 100 and 200, with excellent detail. ISO 400 shows just a touch of softening due to stronger noise reduction, but detail is still excellent. ISO 800 shows a little more luminance noise as well as some additional blurring, though results are still very good. ISO 1,600 also shows an increase in blurring along with higher levels of luminance and chroma noise, but fine detail was still quite good with a tight, film-like noise "grain". Note that these images were shot using the Pentax 645D default "Medium" High ISO Noise Reduction setting.

The Pentax 645D offers very good control over noise reduction applied to its JPEGs. In addition to how much noise reduction is applied ("Off", "Low", "Medium" or "High"), or you can select at what ISO sensitivity it starts (ISO 200, 400, 800, or 1600). The default High-ISO NR Start Level is ISO 400. Of course, the impact of noise and detail loss are highly dependent on the size the photos are printed at, and pixel-peeping on-screen has surprisingly little relationship to how the images look when printed: See the Print Quality section below for recommended maximum print sizes at each ISO.

Extremes: Sunlit, dynamic range and low light tests
Extremely high resolution, though with some clipped highlights. Excellent low-light performance, capable of capturing bright images in near darkness.

Sunlight:
The Pentax 645D struggled a bit in the harsh lighting of the above test. Default contrast is a little high and dynamic range is somewhat limited, so quite a few highlights are clipped in the model's shirt and some of the flowers. Shadow detail is quite good though, if a touch noisy. The +0.3 EV exposure did the best job here, as the default exposure was a bit too dim in the face, and too many highlights were lost at +0.7 EV. Note that these shots were captured with the Pentax 645D's D-Range controls set to their defaults of "Off." (See below for D-Range examples.)

Because digital cameras are more like slide film than negative film (in that they tend to have a more limited tonal range), we test them in the harshest situations to see how they handle scenes with bright highlights and dark shadows, as well as what kind of sensitivity they have in low light. The shot above is designed to mimic the very harsh, contrasty effect of direct noonday sunlight, a very tough challenge for most digital cameras. (You can read details of this test here. In actual shooting conditions, be sure to use fill flash in situations like the one shown here; it's better to shoot in open shade whenever possible.)

Dynamic Range Analysis
A key parameter in a digital camera is its Dynamic Range, the range of brightness that can be faithfully recorded. At the upper end of the tonal scale, dynamic range is dictated by the point at which the RGB data "saturates" at values of 255, 255, 255. At the lower end of the tonal scale, dynamic range is determined by the point at which there ceases to be any useful difference between adjacent tonal steps. Note the use of the qualifier "useful" in there: While it's tempting to evaluate dynamic range as the maximum number of tonal steps that can be discerned at all, that measure of dynamic range has very little relevance to real-world photography. What we care about as photographers is how much detail we can pull out of the shadows before image noise becomes too objectionable. This, of course, is a very subjective matter, and will vary with the application and even the subject matter in question. (Noise will be much more visible in subjects with large areas of flat tints and subtle shading than it would in subjects with strong, highly contrasting surface texture.)

What makes most sense then, is to specify useful dynamic range in terms of the point at which image noise reaches some agreed-upon threshold. To this end, Imatest computes a number of different dynamic range measurements, based on a variety of image noise thresholds. The noise thresholds are specified in terms of f-stops of equivalent luminance variation in the final image file, and dynamic range is computed for noise thresholds of 1.0 (low image quality), 0.5 (medium image quality), 0.25 (medium-high image quality) and 0.1 (high image quality). For most photographers and most applications, the noise thresholds of 0.5 and 0.25 f-stops are probably the most relevant to the production of acceptable-quality finished images, but many noise-sensitive shooters will insist on the 0.1 f-stop limit for their most critical work.

JPEG. The graph at right (click for a larger version) was generated using Imatest's dynamic range analysis for an in-camera Pentax 645D JPEG file with a nominally-exposed density step target (Stouffer 4110) shot at default settings. At ISO 100 (the optimal ISO for dynamic range), the graph shows 10.8 f-stops of total dynamic range, with 7.05 f-stops at the "High" quality level. The High quality score is actually a little below-average for an in-camera JPEG. Compared to the Pentax K-5 which also scored below average at the High quality threshold with its JPEGs, the 645D scored just slightly lower (7.05 vs 7.22 f-stops), and it scored significantly lower compared to some other APS-C models such as the Nikon D7000, which managed a 7.97 f-stop score. Note though that this measurement has a margin of error of about 1/3 f-stop, so differences of less than 0.33 can be ignored, so performance here is similar.

RAW. The graph at right is from the same Stouffer 4110 stepchart image captured as a RAW (.DNG) file, processed with Adobe Camera Raw using the Auto setting, then tweaked manually. As can be seen, the score at the highest quality level increased from 7.05 to 8.88 f-stops, which is almost a two f-stop improvement, while total dynamic range increased about one f-stop to 11.9 from 10.8. These results are good, though not as good as the best APS-C sensors. (The Pentax K-5 for example managed 10.2 f-stops at the highest quality level, and the Nikon D7000 managed 10.1) It's also worth noting here is that ACR's default noise reduction settings reduced overall noise somewhat (see the plot in the lower left-hand corner) relative to the levels in the in-camera JPEG, which would tend to boost the dynamic range numbers for the higher quality thresholds.

Contrast Adjustment
Just as with its saturation adjustment, the Pentax 645D's contrast adjustment offers a fairly wide range of settings (-4 to +4), and the contrast steps are actually a little finer than those for saturation, which is even more to our liking.

At its lowest contrast setting, the 645D did a really excellent job of bringing nice detail out of the shadows as well as preserving a bit more highlight detail in the model's shirt and flowers, but skin tones in the "Outdoor" Portrait were a bit too flat for our tastes, and colors in general in the Far-field House shot were noticeably less saturated.

The series of shots above shows results with several different contrast adjustment settings, showing the minimum step size around zero, as well as both extremes. The camera's contrast adjustment had quite an effect on color saturation, reducing it along with contrast. Contrast and saturation are actually fairly closely coupled, so this is unfortunately not unusual. While you can see the extremes, it's hard to really evaluate contrast on small thumbnails like these, click on any thumbnail to go to the full-size image.

D-Range Settings
The Pentax 645D offers three Shadow Correction levels (Low, Medium, and High) as well as one Highlight Correction setting (On/Off). As the name implies, Shadow Correction works to raise shadow levels while attempting to keep highlights and midtones as they are, and likewise, Highlight Correction attempts to reduce highlights without darkening shadows and midtones. Both can be used simultaneously. See the images below to see their effect on our high contrast "Outdoor" Portrait test shot.

Mouse over the links to see how the various settings for D-Range affects our "Outdoor" Portrait shot. Click on a link to get to the full-res image. (The effect can be a little subtle in shots like those above, so we decided to use a mouse-over to better show how each setting compares to Off.)

Shadow Correction. Above, we see in the images and histograms a gradual lightening of shadows as the Shadow Correction setting is increased, with little impact to highlights.

Highlight Correction. As you can see, Highlight Correction has the opposite effect, toning-down the highlights so that virtually none are clipped, with minimal impact to shadows and midtones.

Note as mentioned above, both Shadow and Highlight Correction can be used simultaneously.

Here are the results with our Far-field House shot. Again, we see a lightening of shadows as the Shadow Correction setting is increased, and a decrease in hot highlights with Highlight Correction.

HDR Capture
The Pentax 645D has a High Dynamic Range (HDR) capture mode where the camera takes three images (underexposed, normal, and overexposed) in quick succession and combines them in-camera into one image.  If performed properly, this method should result in much higher dynamic range, without the additional noise penalty that comes with boosting shadows when using the D-Range option. (In fact, it can reduce shadow noise by combining shadows from the overexposed shot.) There are two HDR settings available: Standard and Strong.

As you can see from the above images, HDR Standard worked reasonably well on our Far-field House test shot, reducing both clipped highlights and bringing out shadow detail. The Strong setting was too much for this scene, though, resulting in very flat and unnatural looking images with reduced saturation. Also keep in mind that your subject needs to be perfectly still during HDR capture, or you'll end up with double images and blurring as can be seen in some of the tree branches in the images above.

Low Light. As expected, the Pentax 645D performed well here, easily able to capture usable images down to the 1/16 foot-candle light level (about 1/16 as bright as average city street lighting at night), at all ISO settings. (Our apologies for the slightly soft images above, however they are still useful for judging low-light performance.) The 645D's metering system struggled a bit with getting the exposure correct at the lowest levels though, as do most cameras, so we used manual exposure for these shots. Color balance with Auto white balance was pretty good with a slightly cool bias at lower ISOs that shifted to a magenta cast at ISO 800 and 1,600 at lower light levels. Noise was quite low all the way up to maximum ISO with default noise reduction, though moderate amounts of luminance and chroma noise were visible when noise reduction was turned off at higher ISOs, but that's to be expected. We did not detect any issues with hot pixels, heat blooming or banding even with long exposure noise reduction disabled.

The Pentax 645D's phase-detection autofocus system was able to focus on our subject down to below the 1/16 foot-candle light level with the smc PENTAX-D FA 645 55mm f/2.8 SDM lens, without the aid of an AF assist lamp. (Keep in mind that the longer shutter speeds here demand the use of a tripod to prevent any blurring from camera movement. A useful trick is to just prop the camera on a convenient surface, and use its self-timer to release the shutter. This avoids any jiggling from your finger pressing the shutter button, and can work quite well when you don't have a tripod handy.)

How bright is this? The one foot-candle light level that this test begins at roughly corresponds to the brightness of typical city street-lighting at night. Cameras performing well at that level should be able to snap good-looking photos of street-lit scenes.

NOTE: This low light test is conducted with a stationary subject, and the camera mounted on a sturdy tripod. Most digital cameras will fail miserably when faced with a moving subject in dim lighting. (For example, a child's ballet recital or a holiday pageant in a gymnasium.) Digital SLRs like the Pentax 645D do much better than point & shoots, but you still shouldn't expect a quick autofocus lock with moving subjects.

Print Quality
ISO 100 shots make excellent 36x48 inches; ISO 400 shots are sharp at 30x40 inches; and ISO 1,600 shots make great 16x20-inch prints.

We had to establish new maximum print sizes for the Pentax 645D, as it's the first 40-megapixel camera we've reviewed. Something tells us it won't be the last, but for now the maximum tested print size is 40x60 inches.

ISO 100 images are what we'd call usable at 40x60 inches, certainly for wall display with some sharpening applied. Straight out of the camera, though, they look better printed at 36x48 inches. That's 3x4 feet. Detail is excellent at this size, as is color.

ISO 200 shots are also quite good printed at 36x48. Very sharp, excellent detail.

ISO 400 images are slightly soft at 36x48, but return to crispness at 30x40.

ISO 800 images print beautifully at 24x36

ISO 1,600 shots take the first (and last) noticeable hit in quality, requiring more noise suppression. While they're usable at 30x40 and quite a bit better at 20x30, they don't quite measure up to the standard of the others until 16x20, still a gigantic print.

Overall the Pentax 645D turns in a stellar performance worthy of a medium-format camera. Image quality is amazingly good, and we were quite conservative of our judgments on print quality. Lowering noise suppression or processing RAW images would likely achieve even larger print sizes with ease.

Testing hundreds of digital cameras, we've found that you can only tell just so much about a camera's image quality by viewing its images on-screen. Ultimately, there's no substitute for printing a lot of images and examining them closely. For this reason, we now routinely print sample images from the cameras we test on our Canon Pro9000 Mark II studio printer, and on the Pixma MP610 here in the office. (See the Canon Pixma Pro9000 Mark II review for details on that model.)